The present invention relates to a vertical synchronization (sync) signal detector for use in a television signal receiver for detecting vertical sync signals included in a composite sync signal which constitutes a part of a television video signal.
Separation of the vertical sync pulses and equalizing pulses from the composite sync signal which includes the horizontal sync pulses, has usually been accomplished with a CR integrating circuit having a relatively large time constant. The separating method is based on the fact that the vertical sync pulses, when integrated at the CR integrating circuit, result in a greater integrated voltage than that of the horizontal sync pulses because the former have greater width. Although this method is extensively used because of the simplicity of the circuit structure, it has a disadvantage because the accurate locating of the horizontal sync pulse becomes difficult. The presence of the sync pulses is detected depending on the gradually inclined charging curve formed by the integrating circuit.
Such a circuit is not applicable, in particular, to the interframe coding system for TV signals where fluctuation in the position of the vertical sync pulses causes a difference between the corresponding picture elements of the interframe even for a static. This results in a determination of transmission efficiency.
The details of the interframe coding system, is described in the "IEEE Transactions on Communications, Vol. Com-23, No. 12," December issue, 1975, pp. 1,461-1,466, and "Proceedings of the IEEE, Vol. 60, No. 7", July issue, 1972, pp. 792-799.